1. Field of the Invention
The present invention relates to lenses for glasses and, more particularly, to an improved multi-layer polarized lens with Rugate filter specifically designed for protective eye wear (prescription and non-prescription glasses and sunglasses) to reduce harmful light transmission and ocular photochemical damage.
2. Description of the Background
The goal of most protective eye wear (including high-end sunglasses) is to provide a particular light transmission profile that yields the highest protection and perfect vision under all light conditions. To accomplish this goal the lenses for protective eye wear often incorporate numerous layers and coatings all of which combine to give a particular profile. The ocular hazards from ultraviolet solar radiation are well established. Ultraviolet radiation falls within a range of wavelengths below visible light, generally between 100 and 400 nanometers. Long UVA radiation occurs at wavelengths between 315 and 400 nanometers. UVB radiation occurs between 280 and 315 nanometers. UVC radiation occurs between 200 and 280 nanometers. Wavelengths between 100 and 200 nanometers are known as vacuum UV. Vacuum UV and UVC are the most harmful to humans, but the earth's ozone layer tends to block these types of ultraviolet radiation. Nevertheless, the occurrence of ocular injury from ultraviolet exposure has increased dramatically over the past few years, and this is thought to be a result of ozone layer depletion.
According to Prevent Blindness America, the American Academy of Ophthalmology, and the American Optometric Association, the hazards from ultraviolet exposure include eyelid cancer, cataract, pterygium, keratitis, and macular degeneration. Cataracts are a major cause of visual impairment and blindness worldwide. “We've found there is no safe dose of UV-B exposure when it comes to risk of cataract, which means people of all ages, races and both sexes should protect their eyes from sunlight year-round.” Infeld, Karen, Sunlight Poses Universal Cataract Risk, Johns Hopkins Study, http://www.eurekalert.org/releases/jhu-sunposcat.html (1998). Likewise, age-related macular degeneration (AMD) is the leading cause of blind registration in the western world, and its prevalence is likely to rise as a consequence of increasing longevity. Beatty et al., The Role of Oxidative Stress in the Pathogenesis of Age-Related Macular Degeneration, Survey of Ophthalmology, volume 45, no. 2 (September–October 2000). A ten-year Beaver Dam Eye Study was recently completed and is reviewed in the Arch Ophthalmology, vol. 122, p. 754–757 (May 2004). This study proves a direct correlation between the incidence of blue light and AMD but no association between UVA and UVB light and AMD.
In view of the above, a lens designed for protective eye wear that dramatically reduces visible blue light combined with a high degree of UVA and UVB protection will preserve visual function. The Food and Drug Administration has recommended that all sunglasses, prescription or non-prescription, block 99% of UVB and 95% of UVA. Most sunglasses on the market meet these criteria. Indeed, there are sunglasses for outdoor enthusiasts that can achieve 99% of both UVA & B reduction.
The American National Standards Institute (ANSI) rates nonprescription eye wear for their potential to protect the human eye against solar radiation. However, many feel that the ANSI Z80.3 standard falls short. For example, the Z80.3 standard does not require specific quantification of the precise transmittance of ultraviolet radiation, nor blue light or infrared radiation, reflected or scattered solar radiation that is not transmitted through the lens but still reaches the human eye. In addition to simply blocking harmful light, a quality lens for protective eye wear will also reduce glare, add contrast, and yet maintain color balance, all to enhance vision. All this requires a lens with an optimum transmission profile that filters the different colors in proportion to their ability to damage the tissue of the retina, thereby reducing the risks of macular degeneration while actually improving vision. The ANSI standards only address one aspect of the lens.
In an effort to develop a more comprehensive method of rating nonprescription eyewear for its ability to protect the eye against solar damage, the FUBI System has been proposed. The system presents a numeric value, from 0 to 100, for each of the three known harmful portions of the solar spectrum: ultraviolet (UV), blue/violet (B), and infrared (IR). A fourth value was determined for the fashion (F) of the eyewear as it relates to protection of the eye against reflected or scattered radiation that is not transmitted through the eyewear. With FUBI, the numeric value of the system for UV, B, and IR is derived by taking the average transmittance of radiation through each tested lens and weighting it by multiplying that value by a relative toxicity factor (RTF) for each waveband of solar radiation tested. The RTF is derived by multiplying the approximate level of radiation reaching a specified anatomic part of the eye at sea level for each wavelength tested by the inverse of the value of its action spectrum (sensitivity) on that part of the eye. This weighted average transmitted percentage of radiation was then deducted from 100 to derive the FUBI value for the UV, B, and IR range. The numeric value for F was derived by measuring the scattered or reflected light from five known sources of luminance at a fixed distance around opacified lenses on each tested frame. The FUBI system has been successfully used to rate a wide variety of known commercial products of nonprescription eyewear.
It is common to provide polarized lenses in sunglasses to eliminate the horizontal transmission of reflected light through the lenses of the glasses to the eyes of the wearer. The polarizing layer blocks light at certain angles, while allowing light to transmit through select angles. This helps to negate annoying glare reflected off other surfaces such as water, snow, automobile windshields, etc. A polarized filter is produced by stretching a thin sheet of polyvinyl alcohol to align the molecular components in parallel rows. The material is passed through an iodine solution, and the iodine molecules likewise align themselves along the rows of polyvinyl alcohol. The sheet of polyvinyl is then applied to the lens with colored rows of iodine oriented vertically in order to eliminate horizontally reflected light. The sheet of polyvinyl may be applied to a lens in one of two ways: the lamination method or the cast-in mold method. To polarize a glass lens, the lamination method is used whereby the polyvinyl filter is sandwiched between two layers of glass. For plastic lenses, the cast-in mold method is used whereby the polyvinyl filter is placed within the lens mold. Relevant prior art patents might be seen in the Schwartz U.S. Pat. No. 3,838,913 and Archambault U.S. Pat. No. 2,813,459. A significant benefit of polarized lenses is the elimination of glare from reflective surfaces such as water.
Rugate filters are a less well-known lens technology in the context of protective eye wear. A Rugate filter is an interference coating in which the refractive index varies continuously in the direction perpendicular to the film plane. The addition of a rugate filter to a lens can block visible blue and UV light, as well as infrared and laser energy, while allowing other visible light to pass unimpeded. Rugate filters are wavelength specific filters that have existed for about a decade. Their simple periodic continuous structures offer a much wider set of spectral responses than discrete structures, and they typically exhibit a spectrum with high reflectivity bands. This allows the possibility of making high reflectivity mirrors with very narrow bandwidth. As an example, Rugate notch filters from Barr The polarizing layer is sandwiched between two optical lens layers such as ophthalmic CR-39 plastic, polycarbonate, glass, Trivex® or high-index. Associates use refractory metal oxides for edge filters and beamsplitters. Rugate filters are typically formed by a continuous deposition process. It is an easy matter to vary the mixture deposited on the substrate, and thus vary the index of refraction. An overview of Rugate filter technology can be found at Johnson et al., “Introduction to Rugate Filter Technology” SPIE Vol. 2046, p. 88–108 (November 1993), inclusive of how a simple rugate filter is derived from Fourier analysis. Other examples can be found in U.S. Pat. No. 5,258,872 “Optical Filter” by W. E. Johnson, et al. and disclosed in U.S. Pat. No. 5,475,531 “Broadband Rugate Filter” by T. D. Rahminow, et al.
In addition to the foregoing, various mirror coatings have been available to the sunglass industry for decades. These mirror coatings can be applied to the front and/or back surface of a lens to further reduce glare and provide protection against infrared rays. Metallic mirrors comprise a layer of metal deposited directly on a glass lens to create the equivalent of a one-way mirror. U.S. Pat. No. 4,070,097 to Gelber, Robert M (1978). However, most metallic oxide coatings have proven to be very susceptible to scratching and wear, especially near salt water. Salt water tends to degrade such coatings over time. In addition, metallic mirror coatings absorb light and generate heat. The more recent advent of dielectric mirror coatings solve some of the above-referenced problems. For one, dielectric coatings reflect light without absorption, thereby avoiding the discomfort of hot glasses. Moreover, dielectric coatings are more durable than metallic oxide coatings, especially in outdoor coastal environments. For example, a dielectric layer having a medium refractive index, e.g., a mixed TiO2 and SiO2 layer, has been used in a rear view mirror. U.S. Pat. No. 5,267,081 to Pein (1993). Similar titanium and quartz dielectric mirror coatings have been applied to glass lenses. In the context of sunglasses, these dielectric mirror coatings of titanium and quartz prevent salt water damage while providing additional reflection of light.
U.S. Pat. Nos. 6,077,569 and 5,846,649 to Knapp et al. suggest a plastic sunglass lens coated with an abrasion resistant material and a dielectric material (including silicon dioxide or titanium oxide). The abrasion-resistant coating layer includes a transparent adhesion layer comprised of C, Si, H, O, and/or N which is deposited by ion-assisted plasma deposition. A second dielectric coating layer is deposited, and a thin metallic mirror layer may be interposed between the abrasion-resistant layer and the dielectric materials to enhance reflectivity and color characteristics. However, the prior art does not teach or suggest how to incorporate a polarizing filter, multi-layer dielectric mirror, and a hydrophobic overcoat in a blue-blocking amber or gray tint lens to provide an outstanding spectroscopic profile, especially for a marine environment.
Hydrophobic coatings are also known in a more general context for protecting lens surfaces (U.S. Pat. No. 5,417,744 to Ameron) and for contact lenses (U.S. Pat. No. 4,569,858 to Barnes Hind). Hydrophobic coatings are also appropriate near water to protect underlying layers of a lens over time. Hydrophobic coatings are especially good for protecting mirrored lenses as above. For example, U.S. Pat. No. 5,928,718 to Dillon discloses a protective coating for reflective sunglasses incorporating a conventional resin/polymer type coating for protection of the mirror finish against abrasion and smudging.
The present inventor has found that a Rugate filter when used in combination with a polarizing layer, with optional dielectric layer and hydrophobic coating, in a lens sandwich configuration yields an exceptional light transmission profile under all light conditions that maximizes the degree of protection as well as clarity of vision, as borne out by the FUBI rating system. The Rugate filter, polarizing layer, and optional dielectric layer and hydrophobic coating are incorporated in a lens sandwich with optical lens layers comprising any one of conventional glass, plastic (CR-39), polycarbonate, Trivex® or high-index plastic or glass layers.
The particular lens layers are a matter of design choice. Glass has a number of advantages in that it is the most scratch-resistant and optically pure material used in ophthalmic lenses. However, glass is about twice the weight of regular (CR-39) plastic and has safety issues. Conventional plastic lenses (CR-39) weigh less than glass lenses and can be tinted to almost any color and density. They are more easily scratched than glass but can have scratch protection applied. Polycarbonate lenses are the most impact resistant lenses available and is commonly used in protective eyewear for sports. Polycarbonate has a high refractive index and is therefore lighter and thinner than conventional plastic lenses. Polycarbonate absorbs all harmful UV light, includes scratch protection and can be made extra thin in the centers and at the edges because of their unique strength. However, polycarbonate is not as optically pure as regular plastic or glass. Trivex® is a relatively new monomer lens material which combines superior optics, impact resistance, and light weight. Trivex® is gaining recognition as delivering the most comprehensive performance of the enumerated lens materials, and yet remains relatively expensive. In addition, high-index plastic layers can be used, albeit they have a high index of refraction and are not as optically correct. Nevertheless, high-index plastic lenses can be made with less material and are thinner and usually lighter weight than regular CR-39 plastic. High-index lenses also absorb all harmful UV light and can be tinted to any shade or color. High-index glass is also available to reduce lens thickness but is considerably heavier.